1. Field of Invention
This invention relates to low melting softening compositions for textiles and textile fibers, particularly for use in automatic laundry dryers.
2. Description of the Related Art
The tendency for laundered textile fibers to acquire stiffness and static charges is most pronounced when the laundry product is a synthetic detergent. Stifness of the fibers and static charges combine to impart a palpable harshness to the textile. Articles of clothing, bed linens and the like, possessing such harshness, are irritating to the skin and uncomfortable. In addition, they tend to retain wrinkles and attract dirt and dust. These undesirable consequences of laundering have been overcome by the use of quaternary ammonium compounds, which are widely used to impart softness and pliability to the textile and to diminish static charges. Quaternary compound softeners may be a component of the laundry detergent, may be added separately to the wash water at some point in the laundry cycle, or dispensed in the dryer.
The utility of quaternary salts of dialkyldiamidoamines, especially those derived from fatty acids, as softeners for textile fibers in laundry wash water applications, and a method for their preparation, are set forth in U.S. Pat. No. 3,492,324. This patent teaches that the quaternary compounds are obtained as semi-solids or solids, which are admixed with appropriate quantities of water to form pastes. These pastes, which are "pourable", may then further be admixed with water to form dispersions suitable for incorporation onto textiles and textile fibers for the purpose of softening them.
Incorporation of fabric softening compositions onto textiles or textile fibers may be accomplished by adding an aqueous dispersion of the fabric softening composition to laundry wash or rinse water. The latter method is widely practiced in home laundries. U.S. Pat. No. 3,442,692 teaches that the inherent problem in adding liquid fabric softening compositions to the rinse cycle in home laundries is that residual soap and/or detergent present may interfere with retention of an effective amount of fabric softening composition by the fiber. Because of the restricted solubility of fabric softening compositions, especially quaternary ammonium compounds, the composition of such liquid laundry products is predominantly water or water and solvent. Liquids are by their nature expensive to store and ship, requiring bulky containers.
The problems inherent in bulky liquid fabric softening compositions may be overcome, as taught by e.g. U.S. Pat. No. 3,442,692, by incorporating the fabric softening composition, as a solution or a dispersion, onto a substrate material, from which the water or water and solvent may be evaporated. Examples of such substrate materials include absorbing paper, sponge, woven or felted fabric. A dry substrate, impregnated with fabric softening composition, may then be added directly to the automatic laundry dryer. In the laundry dryer, the combination of water vapor from the wet laundry, heat, and air flow, are sufficient to distribute the fabric softener onto the laundry articles in the dryer. Thus, a convenient, dry, easily stored and handled fabric softening composition, which uniformly and predictably imparts softening to textile or textile fibers, may be prepared.
An improvement in automatic dryer substrate coating technology is described in U.S. Pat. No. 4,137,345 which teaches the advantages of using a porous, dimensionally stable substrate, onto which a molten fabric softening composition may be coated. Thus, the step of removing water and/or solvent from a fabric softening dispersion or solution impregnated on a substrate is eliminated. The step of drying the substrate is time-consuming and could also cause loss of fabric softening composition from the substrate through volatilization. U.S. Pat. No. 4,137,345 also teaches that a rigid, i.e. dimensionally stable, substrate is preferred, since there will be a marked tendency for a flexible substrate to lose its coating of fabric softening composition through flexure. That is, as the flexible substrate bends and twists within the rotating drum of the automatic laundry dryer, the fabric softening composition on its surface tends to crack, peel, and fall off. The coating of fabric softening compositions onto rigid substrates may be achieved by using fabric softening compositions in the preferred melting range of 60.degree.-90.degree. C.
The melting range of dialkyldiamido quaternary compounds of this invention, such as those described in U.S. Pat. No. 3,492,324, is approximately 95.degree. to 105.degree. C. Moreover, these dialkyldiamido quaternary compounds tend to form friable solids when dried, and thus would not be expected to adhere to a flexible substrate. The viscosity of the dialkyldiamido quaternary compounds of this invention have been measured at 160,000 centipoises at 120.degree. C., which render physically coating onto a substrate difficult. Once coated onto a substrate, dialkyldiamido quaternary compounds would not uniformly or readily be released by the substrate under the conditions existing in automatic laundry dryers. Although dialkyldiamido quaternary ammonium compounds function well as fabric softeners when added to the laundry wash or rinse water, as is known in the art, their physical properties, as set forth above, preclude their direct use in laundry dryers.